This invention relates to a silver halide photographic material containing at least one silver halide emulsion which has enhanced light absorption.
J-aggregating cyanine dyes are used in many photographic systems. It is believed that these dyes adsorb to a silver halide emulsion and pack together on their xe2x80x9cedgexe2x80x9d which allows the maximum number of dye molecules to be placed on the surface. However, a monolayer of dye, even one with as high an extinction coefficient as a J-aggregated cyanine dye, absorbs only a small fraction of the light impinging on it per unit area. The advent of tabular emulsions allowed more dye to be put on the grains due to increased surface area. However, in most photographic systems, it is still the case that not all the available light is being collected.
The need is especially great in the blue spectral region where a combination of low source intensity and relatively low dye extinction result in deficient photoresponse. The need for increased light absorption is also great in the green sensitization of the magenta layer of color negative photographic elements. The eye is most sensitive to the magenta image dye and this layer has the largest, impact on color reproduction. Higher speed in this layer can be used to obtain improved color and image quality characteristics. The cyan layer could also benefit from increased red-light absorption which could allow the use of smaller enulsions with less radiation sensitivity and improved color and image quality characteristics. For certain applications, it may be useful to enhance infrared light absorption in infrared sensitized photographic elements to achieve greater sensitivity and image quality characteristics.
One way to achieve greater light absorption is to increase the amount of spectral sensitizing dye associated with the individual grains beyond monolayer coverage of dye (some proposed approaches are described in the literature, G. R. Bird, Photogr. Sci. Eng., 18, 562 (1974)). One method is to synthesize molecules in which two dye chromophores are covalently connected by a linking group (see U.S. Pat. Nos. 2,518,731, 3,976,493, 3,976,640, 3,622,316, Kokai Sho 64(1989)91134, and EP 565,074). This approach suffers from the fact that when the two dyes are connected they can interfere with each other""s performance, e.g., not aggregating on or adsorbing to the silver halide grain properly.
In a similar approach, several dye polymers were synthesized in which cyanine dyes were tethered to poly-L-lysine (U.S. Pat. No. 4,950,587). These polymers could be combined with a silver halide emulsion, however, they tended to sensitize poorly and dye stain (an unwanted increase in D-min due to retained sensitizing dye after processing) was severe in this system and unacceptable.
A different strategy involves the use of two dyes that are not connected to one another. In this approach the dyes can be added sequentially and are less likely to interfere with one another. Miysaka et al. in EP 270 079 and EP 270 082 describe silver halide photographic material having an emulsion spectrally sensitized with an adsorable sensitizing dye used in combination with a non-adsorable luminescent dye which is located in the gelatin phase of the element. Steiger et al. in U.S. Pat. Nos. 4,040,825 and 4,138,551 describe silver halide photographic material having an emulsion spectrally sensitized with an adsorable sensitizing dye used in combination with second dye which is bonded to gelatin. The problem with these approaches is that unless the dye not adsorbed to the grain is in close proximity to the dye adsorbed on the grain (less than 50 angstroms separation) efficient energy transfer will not occur (see T. Fxc3x6rster, Disc. Faraday Soc., 27, 7 (1959)). Most dye off-the-grain in these systems will not be close enough to the silver halide grain for energy transfer, but will instead absorb light and act as it filter dye leading to a speed loss. A good analysis of the problem with this approach is given by Steiger et al. (Photogr. Sci. Eng., 27, 59 (1983)).
A more useful method is to have two or more dyes form layers on the silver halide grain. Penner and Gilman described the occurrence of greater than monolayer levels of cyanine dye on emulsion grains, Photogr. Sci. Eng., 20, 97 (1976); see also Penner, Photogr. Sci. Eng., 21, 32 (1977). In these cases, the outer dye layer absorbed light at a longer wavelength than the inner dye layer (the layer adsorbed to the silver halide grain). Bird et al. in U.S. Pat. No. 3,622,316 describe a similar system. A requirement was that the outer dye layer absorb light at a shorter wavelength than the inner layer. This appears to be the closest prior art to our invention. The problem with previous dye layering approaches was that the dye layers described produced a very broad sensitization envelope. This would lead to poor color reproduction since, for example, the silver halide grains in the same color record would be sensitive to both green and red light.
Yamashita et. al. (EP 838 719 A2) describes the use of two or more cyanine dyes to form more than one dye layer on silver halide emulsions. The dyes are required to have at least one aromatic or heteroaromatic substituent attached to the chromophore via the nitrogen atoms of the dye. Yamashita et. al. teaches that dye layering will not occur if this requirement is not met. This is undesirable because such substitutents can lead to large amounts of retained dye after processing (dye stain) which affords increased D-min. We have found that this is not necessary and that neither dye is required to have a at least one aromatic or heteroaromatic substitute attached to the chromophore via the nitrogen atoms of the dye.
Not all the available light is being collected in many photographic systems. The need is especially great in the blue spectral region where a combination of low source intensity and relatively low dye extinction result in deficient photoresponse. The need for increased light absorption is also great in the green sensitization of the magenta layer of color negative photographic elements. The eye is most sensitive to the magenta image dye and this layer has the largest impact on color reproduction. Higher speed in this layer can be used to obtain improved color and image quality characteristics. The cyan layer could also benefit from increased red-light absorption which could allow the use of smaller emulsions with less radiation sensitivity and improved color and image quality characteristics. For certain applications, it may be useful to enhance infrared light absorption in infrared sensitized photographic elements to achieve greater sensitivity and image quality characteristics.
We have found that it is possible to form more than one dye layer on silver halide emulsion grains and that this can afford increased light absorption. The dye layers are held together by a non-covalent attractive force such as electrostatic bonding, van der Waals interactions, hydrogen bonding, hydrophobic interactions, dipole-dipole interactions, dipole-induced dipole interactions, London dispersion forces, cationxe2x80x94xcfx80 interactions, etc. or by in situ bond formation. The inner dye layer(s) is absorbed to the silver halide grains and contains at least one spectral sensitizer. The outer dye layer(s) (also referred to herein as an antenna dye layer(s)) absorbs light at an equal or higher energy (equal or shorter wavelength) than the adjacent inner dye layer(s). The light energy emission wavelength of the outer dye layer overlaps with the light energy absorption wavelength of the adjacent inner dye layer.
We have also found that silver halide grains sensitized with at least one dye containing at least one anionic substituent and at least one dye containing at least one, cationic substituent provides increased light absorption.
One aspect of this invention comprises a silver halide photographic material comprising at least one silver halide emulsion comprising silver halide grains having associated therewith at least two dye layers comprising
(a) an inner dye layer adjacent to the silver halide grain and comprising at least one Ae, Dye 1, that is capable of spectrally sensitizing silver halide and
(b) an outer dye layer adjacent to the inner dye layer and comprising at least one dye, Dye 2, wherein Dye 2 is other than a cyanine dye. In preferred embodiments of the invenion Dye 2 is a merocyanine dye, oxonol, dye, arylidene dye, complex merocyanine dye, styryl dye, hemioxonol dye, anthraquinone dye, triphenylmethane dye, azo dye type, azomethine dye, or coumarin dye, wherein the dye layers are held together by non-covalent forces; the outer dye layer adsorbs light at equal or higher energy than the inner dye layer; and the energy emission wavelength of the outer dye layer overlaps with the energy absorption wavelength of the inner dye layer.
Another aspect of this invention comprises a silver halide photographic material comprising at least one silver halide emulsion comprising silver halide grains having associated therewith at least one dye having at least one anionic substituent and at least one dye having at least one cationic substituent, with the proviso that one of the dyes is other than a cyanine dye, preferably a merocyanine dye, oxonol, dye, arylidene dye, complex merocyanine dye, styryl dye, hemioxonol dye, anthraquinone dye, triphenylmethane dye, azo dye type, azomethine dye, or coumarin dye.
The invention provides increased light absorption and photographic sensitivity by forming more than one layer of sensitizing dye on silver halide grains. The increased sensitivity could be used to improve granularity by using smaller emulsions and compensating the loss in speed due to the smaller emulsions by the increased light absorption of the dye layers of the invention. In addition to improved granularity, the smaller emulsions would have lower ionizing radiation sensitivity. Radiation sensitivity is determined by the mass of silver halide per grain. The invention also provides good color reproduction, i.e., no excessive unwanted absorptions in a different color record. Further, the amount of retained dye after processing is minimized by using dyes that do not contain hydrophobic nitrogen substituents and preferably the dyes of the second layer are bleachable dyes. This invention achieves these features whereas methods described in the prior art can not.
As mentioned above, in preferred embodiments of the invention silver halide grains have associated therewith dyes layers that are held together by non-covalent attractive forces. Examples of non-covalent attractive forces include electrostatic attraction, hydrogen-bonding, hydrophobic, and van der Waals interactions or any combinations of these. In addition, in situ bond formation between complimentary chemical groups would be valuable for this invention. For example, one layer of dye containing at least one boronic acid substituent could be formed. Addition of second dye having at least one diol substituent could result in the formation of two dye layers by the in situ formation of boron-diol bonds between the dyes of the two layers. Another example of in situ bond formation would be the formation of a metal complex between dyes that are adsorbed to silver halide and dyes that can form a second or subsequent layer. For example, zirconium could be useful for binding dyes with phosphonate substitutents into dye layers, For a non-silver halide example see H. E. Katz et. al., Science, 254, 1485, (1991).
In a preferred embodiment the current invention uses a combination of a cyanine dye with at least one anionic substituent and a second dye with at least one cationic substituent wherein the second dye is not a cyanine dye. In another preferred embodiment the second dye with at least one cationic substituent is a merocyanine or oxonol dye. It is preferred that the second dye at least partially decolorize during processing to decrease dye stain.
To determine the increased light absorption by the photographic element as a result of forming an outer dye layer in addition to the inner dye layer, it is necessary to compare the overall absorption of the emulsion subsequent to the addition df the dye or dyes of the inner dye layer with the overall absorption of the emulsion subsequent to the further addition of the dye or dyes of the outer dye layer. This measurement of absorption can be done in a variety of ways known in the art, but a particularly convenient and directly applicable method is to measure the absorption spectrum as a function of wavelength of a coating prepared on a planar support from the liquid emulsion in the same manner as is conventionally done for photographic exposure evaluation. The methods of measurement of the total absorption spectrum, in which the absorbed fraction of light incident in a defined manner on a sample as a function of the wavelength of the impinging light for a turbid material such as a photographic emulsion coated onto a planar support, have been described in detail (for example see F. Grum and R. J. Becherer, xe2x80x9cOptical Radiation Measurements, Vol. 1, Radiometryxe2x80x9d, Academic Press, New York, 1979). The absorbed fraction of incident light can be designated by A(xcex), where A is the fraction of incident light absorbed and xcex is the corresponding wavelength of light. Although A(xcex) is itself a useful parameter allowing graphical demonstration of the increase in light absorption resulting from the formation of additional dye layers described in this invention, it is desirable to replace such a graphical comparison with a numerical one. Further, the effectiveness with which the light absorption capability of an emulsion coated on a planar support is converted to photographic image depends, in addition to A(xcex), on the wavelength distribution of the irradiance I(xcex) of the exposing light source. (Irradiance at different wavelengths of light sources can be obtained by well-known measurement techniques. See, for example, F. Grum and R. J. Becherer, xe2x80x9cOptical Radiation Measurements, Vol. 1, Radiometryxe2x80x9d, Academic Press, New York, 1979.) A further refinement follows from the fact that photographic image formation is, like other photochemical processes, a quantum effect so that the irradiance which is usually measured in units of energy per unit time per unit area, needs to be converted into quanta of light N(xcex) via the formula N(xcex)=I(xcex)xcex/hc where h is Planck""s constant and c is the speed of light. Then the number of absorbed photons per unit time per unit area at a given wavelength for a photographic coating is given by: Na(xcex)=A(xcex)N(xcex). In most instances, including the experiments described in the Examples of this invention, photographic exposures are not performed at a single or narrow range of wavelengths but rather simultaneously over a broad spectrum of wavelengths designed to simulate a particular illuminant found in real photographic situations, for example daylight. Therefore the total number of photons of light absorbed per unit time per unit area from such an illuminant consists of a summation or integration of all the values of the individual wavelengths, that is: Na=∫A(xcex)N(xcex)dxcex, where the limits of integration correspond to the wavelength limits of the specified illuminant. In the Examples of this invention, comparison is made on a relative basis between the values of the total number of photons of light absorbed per unit time per unit area of the coating of emulsion containing the sensitizing inner dye layer alone set to a value of 100 and the total number of photons of light absorbed per unit time of the coatings containing an outer dye layer in addition to inner dye layer. These relative values of Na are designated as Normalized Relative Absorption and are tabulated in the Examples. Enhancement of the Normalized Relative Absorption is a quantitative measure of the advantageous light absorption effect of this invention.
As stated in the Background of the Invention, some previous attempts to increase light absorption of emulsions resulted in the presence of dye that was too remote from the emulsion grains to effect energy transfer to the dye adsorbed to the grains, so that a significant increase in photographic sensitivity was not realized. Thus an enhancement in Relative Absorption by an emulsion is alone not a sufficient measurement of the effectiveness of additional dye layers. For this purpose a metric must be defined that relates the enhanced absorption to the resulting increase in photographic sensitivity. Such a parameter is now described.
Photographic sensitivity can be measured in various ways. One method commonly practiced in the art and described in numerous references (for example in The Theory of the Photographic Process, 4th edition, T. H. James, editor, Macmillan Publishing Co., New York, 1977) is to expose an emulsion coated onto a planar substrate for a specified length of time through a filtering element, or tablet interposed between the coated emulsion and light source which modulates the light intensity in a series of uniform steps of constant factors by means of the constructed increasing opacity of the filter elements of the tablet. As a result the exposure of the emulsion coating is spatially reduced by this factor in discontinuous steps in one direction, remaining constant in the orthogonal direction. After exposure for a time required to cause the formation of developable image through a portion but not all the exposure steps, the emulsion coating is processed in an appropriate developer, either black and white or color, and the densities of the image steps are measured with a densitometer. A graph of exposure on a relative or absolute scale, usually in logarithmic form, defined as the irradiance multiplied by the exposure time, plotted against the measured image density can then be constructed. Depending on the purpose, a suitable image density is chosen as reference (for example 0.15 density above that formed in a step which received too low an exposure to form detectable exposure-related image). The exposure required to achieve that reference density can then be determined from the constructed graph, or its electronic counterpart. The inverse of the exposure to reach the reference density is designated as the emulsion coating sensitivity S. The value of Log10S is termed the speed. The exposure can be either monochromatic over a small wavelength range or consist of many wavelengths over a broad spectrum as already described. The film sensitivity of emulsion coatings containing only the inner dye layer or, alternatively, the inner dye layer plus an outer dye layer can be measured as described using a specified light source, for example a simulation of daylight. The photographic sensitivity of a particular example of an emulsion coating containing the inner dye layer plus an outer dye layer can be compared on a relative basis with a corresponding reference of an emulsion coating containing only the inner dye layer by setting S for the latter equal to 100 and multiplying this times the ratio of S for the invention example coating containing an inner dye layer plus outer dye layer to S for the comparison example containing only the inner dye layer. These values are designated as Normalized Relative Sensitivity. They are tabulated in the Examples along with the corresponding speed values. Enhancement of the Normalized Relative Sensitivity is a quantitative measure of the advantageous photographic sensitivity effect of this invention.
As a result of these measurements of emulsion coating absorption and photographic sensitivity, one obtains two sets of parameters for each example, Na and S, each relative to 100 for the comparison example containing only the inner dye layer. The exposure source used to calculate Na should be the same as that used to obtain S. The increase in these parameters Na and S over the value of 100 then represent respectively the increase in absorbed photons and in photographic sensitivity resulting from the addition of an outer dye layer of this invention. These increases are labeled respectively xcex94Na and xcex94S. It is the ratio of xcex94S/xcex94Na that measures the effectiveness of the outer dye layer to increase photographic sensitivity. This ratio, multiplied by 100 to convert to a percentage, is designated the Layering Efficiency, designated E, and is tabulated in the Examples, set forth below along with S and Na. The Layering Efficiency measures the effectiveness of the increased absorption of this invention to increase photographic sensitivity. When either xcex94S or xcex94Na is zero, then the Layering Efficiency is effectively zero.
In preferred embodiments, the following relationship is met:
E=100xcex94S/xcex94Naxe2x89xa710
and
xcex94Naxe2x89xa710
wherein
E is the layering efficiency;
xcex94S is the difference between the Normalized Relative Sensitivity (S) of an emulsion sensitized with the inner dye layer and the Normalized Relative Absorption of an emulsion sensitized with both the inner dye layer and the outer dye layer; and
xcex94Na is the difference between the Normalized Relative Absorption (Na) of an emulsion sensitized with the inner dye layer and the Normalized Relative Absorption of an emulsion sensitized with both the inner dye layer and the outer dye layer.
In order to realize the maximal light capture per unit area of silver halide, it is preferred that the dye or dyes of the outer dye layer (also referred to herein as antenna dye(s), plus any additional dye layers in a multilayer deposition, also be present in a J-aggregated state. For the preferred dyes, the J-aggregated state affords both the highest extinction coefficient and fluorescence yield per unit concentration of dye. Furthermore, extensively J-aggregated secondary cationic dye layers are practically more robust, particularly with respect to desorption and delayering by anionic surfactant-stabilized color coupler dispersions. In addition, when the referred dyes are layered above a conventional cyanine sensitizing dye of opposite charge which is adsorbed directly to the silver halide surface, the inherent structural dissimilarity of the two dye classes minimizes co-adsorption and dye mixing (e.g., cyanine dye plus merocyanine dye) on the grain. Uncontroled surface co-aggregation between dyes of opposite charge (e.g. anionic cyanine plus cationic cyanine) can result in a variety of undesirable photographic effects, such as severe desensitization.
In one preferred embodiment, the antenna dye layer can form a well-ordered liquid-crystalline phase (a lyotropic mesophase) in aqueous media (e.g. water, aqueous gelatin, methanolic aqueous gelatin etc.), and preferably forms a smectic liquid-crystalline phase (W. J.Harrison, D. L. Mateer and G. J. T. Tiddy, J.Phys.Chem. 1996, 100, pp 2310-2321). More specifically, in one embodiment preferred antenna dyes will form liquid-crystalline J-aggregates in aqueous-eased media (in the absence of silver halide grains) at any equivalent molar concentration equal to, or 4 orders of magnitude greater than, but more preferably at any equivalent molar concentration equal to or less than, the optimum level of primary silver halide-adsorbed dye deployed for conventional sensitization (see The Theory of the Photographic Process, 4th edition, T. H. James, editor, Macmillan Publishing Co., New York, 1977, for a discussion of aggregation).
Mesophase-forming dyes may be readily identified by someone skilled in the art using polarized-light optical microscopy as described by N. H. Hartshorne in The Microscopy of Liquid Crystals, Microscope Publications Ltd., London, 1974. In one embodiment, preferred antenna dyes when dispersed in the aqueous medium of choice (including water, aqueous gelatin, aqueous methanol etc. with or without dissolved electrolytes, buffers, surfactants and other common sensitization addenda) at optimum concentration and temperature and viewed in polarized light as thin films sandwiched between a glass microscope slide and cover slip display the birefringence textures, patterns and flow rheology characteristic of distinct and readily identifiable structural types of mesophase (e.g. smectic, nematic, hexagonal). Furthermore, in one embodiment, the preferred dyes when dispersed in the aqueous medium as a liquid-crystalline phase generally exhibit J-aggregation resulting in a unique bathochromically shifted spectral absorption band yielding high fluorescence intensity. In another embodiment useful hypsochromically shifted spectral absorption bands may also result from the stabilization of a liquid-crystalline phase of certain other preferred dyes. In certain other embodiments of dye layering, especially in the case of dye layering via in situ bond formation, it may be desirable to use antenna dyes that do not aggregate.
In another preferred embodiment the second layer comprises a mixture of merocyanine dyes. Wherein at least one merocyanine has a cationic substituent and at least one merocyanine dye has an anionic substituent. Merocyanine dyes with anionic substituents are well know in the literature (see Hamer, (Cyanine Dyes and Related Compounds, 1964 (publisher John Wiley and Sons, New York, N.Y.)). Merocyanine dyes with cationic substituents have been described in U.S. Pat. No. 4,028,353.
In a preferred embodiment, the first dye layer comprises one or more cyanine dyes. Preferably the cyanine dyes have at least one negatively charged substituent. In another preferred embodiment, the second dye layer comprises one or more merocyanine dyes. Preferably the merocyanine dyes have at least one positively charged substituent. More preferably the second dye layer consists of a mixture of merocyanine dyes that have at least one positively charged substituent and merocyanine dyes that have at least one negatively charged substituent.
The dye or dyes of the first layer are added at a level such that, along with any other adsorbants (e.g., antifogants), they will substantially cover at least 80% and more preferably 90% of the surface of the silver halide grain. The area a dye covers on the silver halide surface can be determined preparing a dye concentration series and choosing the dye level for optimum performance or by well-known techniques such as dye adsorption isotherms (for example see W. West, B. H. Carroll, and D. H. Whitcomb, J. Phys. Chem, 56, 1054 (1962)).
For green light absorbing dyes a preferred embodiment is that at least one dye of the first layer contain a benzoxazole nucleus. The benzoxazole nucleus is independently substituted with an aromatic substituent, such as a phenyl group, a pyrrole group, etc.
In some cases, during dye addition and sensitization of the silver halide emulsion, it appears that excess gelatin can interfere with the dye layer formation. In some cases, it is preferred to keep the gelatin levels below 8% and preferably below 4% by weight. Additional gelatin can be added after the dye layers have formed.
In one preferred embodiment, a molecule containing a group that strongly bonds to silver halide, such as a mercapto group (or a molecule that forms a mercapto group under alkaline or acidic conditions) or a thiocarbonyl group is added after the first dye layer has been formed and before the second dye layer is formed. Mercapto compounds represented by the following formula (A) are particularly preferred. 
wherein R6 represents an alkyl group, an alkenyl group or an aryl group and Z4 represents a hydrogen atom, an alkali metal atom, an ammonium group or a protecting group that can be removed under alkaline or acidic conditions. Examples of some preferred mercapto compounds are shown below. 
In describing preferred embodiments of the invention, one dye layer is described as an inner layer and one dye layer is described as an outer layer. It is to be understood that one or more intermediate dye layers may be present between the inner and outer dye layers, in which all of the layers are held together by non-covalent forces, as discussed in more detail above. Further, the dye layers need not completely encompass the silver halide grains of underlying dye layer(s). Also some mixing of the dyes between layers is possible.
The dyes of the first dye layer are any dyes capable of spectrally sensitizing a silver halide emulsion, for example, a cyanine dye, merocyanine dye, complex cyanine dye, complex merocyanine dye, homopolar cyanine dye, or hemicyanine dye, etc. Of these dyes, merocyanine dyes containing a thiocarbonyl group and cyanine dyes are particularly useful. Of these, cyanine dyes are especially useful. Particularly preferred as dyes for the first layer are cyanine dyes of Formula Ia or merocyanine dyes of Formula Ib. 
wherein:
E1 and E2 may be the same or different and represent the atoms necessary to form a substituted or unsubstituted heterocyclic ring which is a basic nucleus (see The Theory of the Photographic Process, 4th edition, T. H. James, editor, Macmillan Publishing Co., New York, 1977 for a definition of basic and acidic nucleus),
each J independently represents a substituted or unsubstituted methine group,
q is a positive integer of from 1 to 4,
p and r each independently represents 0 or 1,
D1 and D2 each independently represents substituted or unsubstituted alkyl or unsubstituted aryl and at least one of D1 and D2 contains an anionic substituent,
W2 is one or more a counterions as necessary to balance the charge; 
wherein E1, D1, J, p, q and W2 are as defined above for formula (Ia) wherein E4 represents the atoms necessary to complete a substituted or unsubstituted heterocycic acidic nucleus which preferably contains a thiocarbonyl;
In another preferred embodiment the inner dye layer contains at least one dye of Formula Ic: 
wherein:
G1, G1xe2x80x2 and E1 independently represent the non-metallic atoms required to complete a substituted or unsubstituted ring system containing at least one 5- or 6-membered heterocyclic nucleus; n is a positive integer from 1 to 4, each L independently represents a substituted or unsubstituted methine group, R1 and R1xe2x80x2 each independently represents a substituted or unsubstituted aryl or substituted or unsubstituted aliphatic group, at least one of R1 and R1xe2x80x2 has a negative charge, and W1 is a counterion if necessary to balance the charge.
In another preferred embodiment the inner dye layer contains at least one dye of Formula Id: 
wherein:
X1, X2, independently represent S, Se, O, or Nxe2x80x94Rxe2x80x2, Z1, Z2, each contains independently at least one aromatic group, the dyes can be further substituted, R is hydrogen, substituted or unsubstituted lower alkyl, aryl, alkylaryl, R1 and R2 each independently represents a substituted or unsubstituted aryl or a substituted or unsubstituted aliphatic group, at least one of R1 and R2 has a negative charge, and W1 is a cationic counterion if needed to balance the charge.
The dyes of the second dye layer do not need to be capable of spectrally sensitizing a silver halide emulsion. Some preferred dyes are merocyanine dyes, arylidene dyes, complex merocyanine dyes, hemioxonol dyes, oxonol dyes, triphenylmethane dyes, azo dye types, azomethines or others. It is preferable to have a positively charged dye present in the second layer and more preferably to have both a positively and negatively charged dye present in the second layer
Particularly preferred as dyes for the second layer are dyes having structure IIa and IIb, IIIa, and IIIb. 
wherein E1, D1, J, p, q and W2 are as defined above for formula (I) and G represents 
wherein E4 represents the atoms necessary to complete a substituted or unsubstituted heterocyclic acidic nucleus which preferably does not contain a thiocarbonyl, and F and Fxe2x80x2 each independently represents a cyano radical, an ester radical, an acyl radical, a carbamoyl radical or an alkylsulfonyl radical; and at least one of D1, E1, J, or G has a substituent containing a positive charge, 
wherein E1, D1, J, p, q G and W2 are as defined above for formula (IIa) and except that at least one of D1, E1, J, or G has a substituent containing a negative charge instead of a positive charge, 
wherein J and W2 are as defined above for formula (I) above and q is 2,3 or 4, and E and E6 independently represent the atoms necessary to complete a substituted or unsubstituted acidic heterocyclic nucleus, and at least one of E5, E6 or J is has a substituent that has a positive charge. 
wherein E5, E6, J and W2 are as defined above for formula (IIb) and at least one of E5, E6 or J is has a substituent that has a negative charge instead of a positive charge.
In another preferred embodiment the outer dye layer contains at least one dye of Formula IIc: 
wherein:
R5 represents a substituted or unsubstituted aromatic or heteroaromatic group, a substituted or unsubstituted alkyl or hydrogen, R6 represents a substituted or unsubstituted aryl or substituted or unsubstituted aliphatic group, G2 represent the non-metallic atoms required to complete a substituted or unsubstituted ring system containing at least one 5- or 6-membered heterocyclic nucleus, m may be 0, 1, 2, or 3, E1 represents an electron-withdrawing group; at least one of R5, L5, L6, G2 or R6 has a substituent with a positive charge, and W2 is one or more anionic counterions necessary to balance the charge.
In another preferred embodiment the outer dye layer contains at least one dye of Formula IId: 
wherein:
X5 independently represent S, Se, O, Nxe2x80x94Rxe2x80x2, or C(RaRb), E1 represents an electron-withdrawing group, R8 represents a substituted or unsubstituted aromatic or heteroaromatic group, a substituted or unsubstituted alkyl or hydrogen, L5, L6, L7, L8 independently represents a substituted or unsubstituted methine group,
m may be 1, or 2, Z6 is hydrogen or a substituent, at least one of R8, L5, L6, Z5, or R9 has a substituent with a positive charge, and W3 is one or more anionic counterions necessary to balance the charge.
In another preferred embodiment the outer dye layer contains at least one dye of Formula IIe: 
wherein
Z1 represents a halogen, substituted or unsubstituted aromatic or heteroaromatic group, a fused aromatic ring, substituted or unsubstituted amide, ester, alkyl or aryl group, Z2 represents a substituted or unsubstituted aromatic or heteroaromatic group, R1 represents a substituted or unsubstituted alkyl group containing a cationic substituent, L1 and L2 represent hydrogen, or substituted or unsubstituted alkyl or aryl, and W is an anionic counterion.
In another preferred embodiment the outer dye layer contains at least one dye of Formula IIf: 
wherein:
Z1xe2x80x2 represents a halogen, a substituted or unsubstituted aromatic or heteroaromatic group, a substituted or unsubstituted aromatic or heteroaromatic group that is linked to the dye by an amide or ester group, or a fused aromatic ring, Z2xe2x80x2 represents a substituted or unsubstituted aromatic or heteroaromatic group, R1xe2x80x2 represents a substituted or unsubstittuted alkyl or aryl group containing an anionic substituent, L1xe2x80x2 and L2xe2x80x2 represents hydrogen, or a substituted or unsubstituted alkyl or aryl, and W is an cationic counterion.
Examples of negatively charged substituents are 3-sulfopropyl, 2-carboxyethyl, 4-sulfobutyl, etc. Examples of positively charged substituents are 3-(trimethylammonio)propyl), 3-(4-ammoniobutyl), 3-(4-guanidinobutyl) etc. Other examples are any substitutents that take on a positive charge in the silver halide emulsion melt, for example, by protonation such as aminoalkyl substitutents, e.g. 3-(3-aminopropyl), 3-(3-dimethylaminopropyl), 4-(4-methylaminopropyl), etc.
When reference in this application is made to a particular moiety as a xe2x80x9cgroupxe2x80x9d, this means that the moiety may itself be unsubstituted or substituted with one or more substituents (up to the maximum possible number). For example, xe2x80x9calkyl groupxe2x80x9d refers to a substituted or unsubstituted alkyl, while xe2x80x9cbenzene groupxe2x80x9d refers to a substituted or unsubstituted benzene (with up to six substituents). Generally, unless otherwise specifically stated, substituent groups usable on molecules herein include any groups, whether substituted or unsubstituted, which do not destroy properties necessary for the photographic utility. Examples of substituents on any of the mentioned groups can include known substituents, such as: halogen, for example, chloro, fluoro, bromo, iodo; alkoxy, particularly those xe2x80x9clower alkylxe2x80x9d (that is, with 1 to 6 carbon atoms, for example, methoxy, ethoxy; substituted or unsubstituted alkyl, particularly lower alkyl (for example, methyl, trifluoromethyl); thioalkyl (for example, methylthio or ethylthio), particularly either of those with 1 to 6 carbon atoms; substituted and unsubstituted aryl, particularly those having from 6 to 20 carbon atoms (for examples phenyl); and substituted or unsubstituted heteroaryl, particularly those having a 5 or 6-membered ring containing 1 to 3 heteroatoms selected from N, O, or S (for example, pyridyl, thienyl, furyl, pyrrolyl); acid or acid salt groups such as any of those described below; and others known in the art. Alkyl substituents may specifically include xe2x80x9clower alkylxe2x80x9d (that is, having 1-6 carbon atoms), for example, methyl, ethyl, and the like. Further, with regard to any alkyl group or alkylene group, it will be understood that these can be branched or unbranched and include ring structures.
Examples of suitable dye structures are listed below in Table I.
Other non-cyanine dyes that can be used for the outer dye layer in accordance with this invention include, for example:
an oxonol dye of Formula IV: 
wherein A1 and A2 are ketomethylene or activated methylene moieties, L1-L7 are substituted or unsubstituted methine groups, (including the possibility of any of them being members of a five or six-membered ring where at least one and preferably more than one of p, q, or r is 1); M+ is a cation, and p, q and r are independently 0 or 1;
an oxonol dye of Formulae IV-A or IV-B: 
wherein W1 and Y1 are the atoms required to form a cyclic activated methylene/ketomethylene moiety; R3 and R5 are aromatic or heteroaromatic groups; R4 and R6 are electron-withdrawing groups; G1 to G4 is O or dicyanovinyl (xe2x80x94C(CN)2)) and p, q, and r are defined as above, and L1 to L7 are defined as above;
An oxonol dye of Formula V 
wherein X is oxygen or sulfur; R7-R10 each independently represent an unsubstituted or substituted alkyl group, an unsubstituted or substituted aryl group or an unsubstituted or substituted heteroaryl group; L1, L2 and L3 each independently represent substituted or unsubstituted methine groups; M+ represents a proton or an inorganic or organic cation; and n is 0, 1, 2 or 3;
a merocyanine of Formula VI: 
wherein A3 is a ketomethylene or activated methylene moiety as described above; each L8 to L15 are substituted or unsubstituted methine groups (including the possibility of any of them being members of a five or six-membered ring where at least one and preferably more than 1 of s, t, v or w is 1); Z1 represents the non-metallic atoms necessary to complete a substituted or unsubstituted ring system containing at least one 5 or 6-membered heterocyclic nucleus; R17 represents a substituted or unsubstituted alkyl, aryl, or aralkyl group;
a merocyanine dye of Formula VII-A: 
wherein A4 is an activated methylene moeity or a ketomethylene moeity as described above, R18 is substituted or unsubstituted aryl, alkyl or aralkyl, R19 to R22 each individually represent hydrogen, alkyl, cycloalkyl, alkeneyl, substituted or unsubstituted aryl, heteroaryl or aralkyl, alkylthio, hydroxy, hydroxylate, alkoxy, amino, alkylamino, halogen, cyano, nitro, carboxy, acyl, alkoxycarbonyl, aminocarbonyl, sulfonamido, sulfamoyl, including the atoms required to form fused aromatic or heteroaromatic rings, or groups containing solubilizing substituents as described above for Y. L8 through L13 are methine groups as described above for L1 through L7, Y2 is O, S, Te, Se, NRx, or CRyRz(where Rx, Ry and Rz are alkyl groups with 1-5 carbons), and s and t and v are independently 0 or 1;
a merocyanine dye of Formula VIII-A: 
wherein R23 is a substituted or unsubstituted aryl, heteroaryl, or a substituted or unsubstituted amino group; G5 is O or dicyanovinyl (C(CN)2), E1 is an electron-withdrawing group, R18 to R22, L8 to L13, Y2, and s, t and v are as described above;
a dye of Formula VIII-B: 
wherein G6 is oxygen (O) or dicyanovinyl (C(CN)2),R9 to R12 groups each individually represent groups as described above, and R18, R19 through R22, Y2, L8 through L13, and s, t and v are as described above,
a dye of Formula VIII-C: 
wherein R25 groups each individually represent the groups described for R19 through R22 above, Y3 represents O, S, NRx, or CRyRz(where Rx, Ry and Rz are alkyl groups with 1-5 carbons), x is 0, 1, 2, 3 or 4, R24 represents aryl, alkyl or acyl, and Y2, R18, R19 through R22, L8 through L13, and, s, t and v are as described above;
a dye of Formula VIII-D: 
wherein E2 represents an electron-withdrawing group, preferably cyano, R26 represents aryl, alkyl or acyl, and Y2, R18, R19 through R22, L8 through L13, and, s, t and v are as described above;
a dye of Formula VIII-E: 
wherein R27 is a hydrogen, substituted or unsubstituted alkyl, aryl or aralkyl, R28 is substituted or unsubstituted alkyl, aryl or aralkyl, alkoxy, amino, acyl, alkoxycarbonyl, carboxy, carboxylate, cyano, or nitro; R18 to R22, L8 to L13, Y2, and s, t and v are as described above;
a dye of Formula VIII-F: 
wherein R29 and R30 are each independently a hydrogen, substituted or unsubstituted alkyl, aryl or aralkyl, Y4 is O or S, R18 to R22, L8 to L13, Y2, and s, t and v are is described above;
a dye of Formula IX: 
wherein A5 is a ketomethylene or activated methylene, L16 through L18 are substituted or unsubstituted methine, R31 is alkyl, aryl or aralkyl, Q3 represents the non-metallic atoms necessary to complete a substituted or unsubstituted ring system containing at least one 5- or 6-membered heterocyclic nucleus, R32 represents groups as described above for R19 to R22, y is 0, 1, 2, 3 or 4, z is 0, 1 or 2;
a dye of Formula X: 
wherein A6 is a ketomethylene or activated methylene, L16 through L18 are methine groups as described above for L1 through L7, R33 is substituted or unsubstituted alkyl, aryl or aralkyl, R34 is substituted or unsubstituted aryl, alkyl or aralkyl, R35 groups each independently represent groups as described for R19 through R22, z is 0, 1 or 2, and a is 0, 1,2, 3 or 4;
a dye of Formula XI: 
wherein A7 represents a ketomethylene or activated methylene moiety, L19 through L21 represent methine groups as described above for L1 through L7, R36 groups each individually represent the groups as described above for R19 through R22, b represents 0 or 1, and c represents 0, 1, 2, 3 or 4;
a dye of Formula XII: 
wherein A8 is a ketomethylene or activated methylene, L19 through L21 and b are as described above, R39 groups each individually represent the groups as described above for R19 through R22, and R37 and R38 each individually represent the groups as described for R18 above, and d represents 0, 1, 2, 3 or 4;
a dye of Formula XIII: 
wherein A9 is a ketomethylene or activated methylene moiety, L22 through L24 are methine groups as described above for L1 through L7, e is 0 or 1, R40 groups each individually represent the groups described above for R19 through R22, and f is 0, 1, 2, 3 or 4;
a dye of Formula XIV: 
wherein A10 is a ketomethylene or activated methylene moiety, L25 through L27 are methine groups as described above for L1 through L7, g is 0, 1 or 2, and R37 and R38 each individually represent the groups described above for R18;
a dye of Formula XV: 
wherein A11 is a ketomethylene or activated methylene moiety, R41 groups each individually represent the groups described above for R19 through R22, R37 and R38 each represent the groups described for R18, and h is 0, 1, 2, 3, or 4;
a dye of Formula XVI:
Q4xe2x80x94Nxe2x95x90Nxe2x80x94Q5xe2x80x83xe2x80x83Formula XVI
wherein Q4 and Q5 each represents the atoms necessary to form at least one heterocyclic or carbocyclic, fused or unfused 5 or 6-membered-ring conjugated with the azo linkage;.
Dyes of Formula IV-XVI above are preferably substituted with either a cationic or an anionic group.
The emulsion layer of the photographic element of the invention can comprise any one or more of the light sensitive layers of the photographic element. The photographic elements made in accordance with the present invention can be black and white elements, single color elements or multicolor elements. Multicolor elements contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer.
Photographic elements of the present invention may also usefully include a magnetic recording material as described in Research Disclosure, Item 34390, November 1992, or a transparent magnetic recording layer such as a layer containing magnetic particles on the underside of a transparent support as in U.S. Pat. Nos. 4,279,945 and 4,302,523. The element typically will have a total thickness (excluding the support) of from 5 to 30 microns. While the order of the color sensitive layers can be varied, they will normally be red-sensitive, green-sensitive and blue-sensitive, in that order on a transparent support, (that is, blue sensitive furthest from the support) and the reverse order on a reflective support being typical.
The present invention also contemplates the use of photographic elements of the present invention in what are often referred to as single use cameras (or xe2x80x9cfilm with lensxe2x80x9d units). These cameras are sold with film preloaded in them and the entire camera is returned to a processor with the exposed film remaining inside the camera. Such cameras may have glass or plastic lenses through which the photographic element is exposed.
In the following discussion of suitable materials for use in elements of this invention, reference will be made to Research Disclosure, September 1996, Number 389, Item 38957, which will be identified hereafter by the term xe2x80x9cResearch Disclosure I.xe2x80x9d The Sections hereafter referred to are Sections of the Research Disclosure I unless otherwise indicated. All Research Disclosures referenced are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND. The foregoing references and all other references cited in this application, are incorporated herein by reference.
The silver halide emulsions employed in the photographic elements of the present invention may be negative-working, such as surface-sensitive emulsions or unfogged internal latent image forming emulsions, or positive working emulsions of the internal latent image forming type (that are fogged during processing). Suitable emulsions and their preparation as well as methods of chemical and spectral sensitization are described in Sections I through V. Color materials and development modifiers are described in Sections V through XX. Vehicles which can be used in the photographic elements are described in Section II, and various additives such as brighteners, antifoggants, stabilizers, light absorbing and scattering materials, hardeners, coating aids, plasticizers, lubricants and matting agents are described, for example, in Sections VI through XIII. Manufacturing methods are described in all of the sections, layer arrangements particularly in Section XI, exposure alternatives in Section XVI, and processing methods and agents in Sections XIX and XX.
With negative working silver halide a negative image can be formed. Optionally a positive (or reversal) image can be formed although a negative image is typically first formed.
The photographic elements of the present invention may also use colored couplers (e.g. to adjust levels of interlayer correction) and masking couplers such as those described in EP 213 490; Japanese Published Application 58-172,647; U.S. Pat. No. 2,983,608; German Application DE 2,706,117C; U.K. Patent 1,530,272; Japanese Application A-113935; U.S. Pat. No. 4,070,191 and German Application DE 2,643,965. The masking couplers may be shifted or blocked.
The photographic elements may also contain materials that accelerate or otherwise modify the processing steps of bleaching or fixing to improve the quality of the image. Bleach accelerators described in EP 193 389; EP 301 477; U.S. Pat. Nos. 4,163,669; 4,865,956; and 4,923,784 are particularly useful. Also contemplated is the use of nucleating agents, development accelerators or their precursors (UK Patent 2,097,140; U.K. Patent 2,131,188); development inhibitors and their precursors (U.S. Pat. Nos. 5,460,932; 5,478,711); electron transfer agents (U.S. Pat. Nos. 4,859,578; 4,912,025); antifoggong and anti color-mixing agents such as derivatives of hydroquinones, aminophenols, amines, gallic acid; catechol; ascorbic acid; hydrazides; sulfonamidophenols; and non color-forming couplers.
The elements may also contain filter dye layers comprising colloidal silver sol or yellow and/or magenta filter dyes and/or antihalation dyes (particularly in an undercoat beneath all light sensitive layers or in the side of the support opposite that on which all light sensitive layers are located) either as oil-in-water dispersions, latex dispersions or as solid particle dispersions. Additionally, they may be used with xe2x80x9csmearingxe2x80x9d couplers (e.g. as described in U.S. Pat. No. 4,366,237; EP 096 570; U.S. Pat. Nos. 4,420,556; and 4,543,323.) Also, the couplers may be blocked or coated in protected form as described, for example, in Japanese Application 61/258,249 or U.S. Pat. No. 5,019,492.
The photographic elements may further contain other image-modifying compounds such as xe2x80x9cDevelopment Inhibitor-Releasingxe2x80x9d compounds (DIR""s). Useful additional DIR""s for elements of the present invention, are known in the art and examples are described in U.S. Pat. Nos. 3,137,578; 3,148,022; 3,148,062; 3,227,554; 3,384,657; 3,379,529; 3,615,506; 3,617,291; 3,620,746; 3,701,783, 3,733,201; 4,049,455; 4,095,984; 4,126,459; 4,149,886; 4,150,228; 4,211,562; 4,248,962; 4,259,437; 4,362,878; 4,409,323; 4,477,563; 4,782,012; 4,962,018; 4,500,634; 4,579,816; 4,607,004; 4,618,571; 4,678,739; 4,746,600; 4,746,601; 4,791,049; 4,857,447; 4,865,959; 4,880,342; 4,886,736; 4,937,179; 4,946,767; 4,948,716; 4,952,485; 4,956,269; 4,959,299; 4,966,835; 4,985,336 as well as in patent publications GB 1,560,240; GB 2,007,662; GB 2,032,914; GB 2,099,167; DE 2,842,063, DE 2,937,127; DE 3,636,824; DE 3,644,416 as well as the following European Patent Publications: 272,573; 335,319; 336,411; 346,899; 362,870; 365,252; 365,346; 373,382; 376,212; 377,463; 378,236; 384,670; 396,486; 401,612; 401,613.
DIR compounds are also disclosed in xe2x80x9cDeveloper-Inhibitor-Releasing (DIR) Couplers for Color Photography,xe2x80x9d C. R. Barr, J. R. Thirtle and P. W. Vittum in Photographic Science and Engineering, Vol. 13, p. 174 (1969), incorporated herein by reference.
It is also contemplated that the concepts of the present invention may be employed to obtain reflection color prints as described in Research Disclosure, November 1979, Item 18716, available from Kenneth Mason Publications, Ltd, Dudley Annex, 12a North Street, Emsworth, Hampshire P0101 7DQ, England, incorporated herein by reference. The emulsions and materials to form elements of the present invention, may be coated on pH adjusted support as described in U.S. Pat. No. 4,917,994; with epoxy solvents (EP 0 164 961); with additional stabilizers (as described, for example, in U.S. Pat. Nos. 4,346,165; 4,540,653 and 4,906,559); with ballasted chelating agents such as those in U.S. Pat. No. 4,994,359 to reduce sensitivity to polyvalent cations such as calcium; and with stain reducing compounds such as described in U.S. Pat. Nos. 5,068,171 and 5,096,805. Other compounds which may be useful in the elements of the invention are disclosed in Japanese Published Applications 83-09,959; 83-62,586; 90-072,629; 90-072,630; 90-072,632; 90-072,633; 90-072,634; 90-077,822; 90-078,229; 90-078,230; 90-079,336; 90-079,338; 90-079,690; 90-079,691; 90-080,487; 90-080,489; 90-080,490; 90080,491; 90-080,492; 90-080,494; 90-085,928; 90-086,669; 90-086,670; 90-087,361; 90-087,362; 90-087,363; 90-087,364; 90-088,096; 90-088,097; 90-093,662; 90-093,663; 90-093,664; 90-093,665; 90-093,666; 90-093,668; 90-094,055; 90-094,056; 90-101,937; 90-103,409; 90-151,577.
The silver halide used in the photographic elements may be silver iodobromide, silver bromide, silver chloride, silver chlorobromide, silver chloroiodobromide, and the like.
The type of silver halide grains preferably include polymorphic, cubic, and octahedral. The grain size of the silver halide may have any distribution known to be useful in photographic compositions, and may be either polydipersed or monodispersed. Tabular grain silver halide emulsions may also be used.
The silver halide grains to be used in the invention may be prepared according to methods known in the art, such as those described in Research Disclosure I and The Theory of the Photographic Process, 4th edition, T. H. James, editor, Macmillan Publishing Co., New York, 1977. These include methods such as ammoniacal emulsion making, neutral or acidic emulsion making, and others known in the art. These methods generally involve mixing a water soluble silver salt with a water soluble halide salt in the presence of a protective colloid, and controlling the temperature, pAg, pH values, etc, at suitable values during formation of the silver halide by precipitation.
In the course of grain precipitation one or more dopants (grain occlusions other than silver and halide) can be introduced to modify grain properties. For example, any of the various conventional dopants disclosed in Research Disclosure, Item 38957, Section I. Emulsion grains and their preparation, sub-section G. Grain modifying conditions and adjustments, paragraphs (3), (4) and (5), can be present in the emulsions of the invention. In addition it is specifically contemplated to dope the grains with transition metal hexaco-ordination complexes containing one or more organic ligands, as taught by Olm et al U.S. Pat. No. 5,360,712, the disclosure of which is here incorporated by reference.
It is specifically contemplated to incorporate in the face centered cubic crystal lattice of the grains a dopant capable of increasing imaging speed by forming a shallow electron trap (hereinafter also referred to as a SET) as discussed in Research Disclosure Item 36736 published November 1994, here incorporated by reference.
The SET dopants are effective at any location within the grains. Generally better results are obtained when the SET dopant is incorporated in the exterior 50 percent of the grain, based on silver. An optimum grain region for SET incorporation is that formed by silver ranging from 50 to 85 percent of total silver forming the grains. The SET can be introduced all at once or run into the reaction vessel over a period of time while grain precipitation is continuing. Generally SET forming dopants are contemplated to be incorporated in concentrations of at least 1xc3x9710xe2x88x927 mole per silver mole up to their solubility limit, typically up to about 5xc3x9710xe2x88x924 mole per silver mole.
SET dopants are known to be effective to reduce reciprocity failure. In particular the use of iridium hexacoordination complexes or lr+4 complexes as SET dopants is advantageous.
Iridium dopants that are ineffective to provide shallow electron traps (non-SET dopants) can also be incorporated into the grains of the silver halide grain emulsions to reduce reciprocity failure.
To be effective for reciprocity improvement the Ir can be present at any location within the grain structure. A preferred location within the grain structure for Ir dopants to produce reciprocity improvement is in the region of the grains formed after the first 60 percent and before the final 1 percent (most preferably before the final 3 percent) of total silver forming the grains has been precipitated. The dopant can be introduced all at once or run into the reaction vessel over a period of time while grain precipitation is continuing. Generally reciprocity improving non-SET Ir dopants are contemplated to be incorporated at their lowest effective concentrations.
The contrast of the photographic element can be further increased by doping the grains with a hexacoordination complex containing a nitrosyl or thionitrosyl ligand (NZ dopants) as disclosed in McDugle et al U.S. Pat. No. 4,933,272, the disclosure of which is here incorporated by reference.
The contrast increasing dopants can be incorporated in the grain structure at any convenient location. However, if the NZ dopant is present at the surface of the grain, it can reduce the sensitivity of the grains. It is therefore preferred that the NZ dopants be located in the grain so that they are separated from the grain surface by at least 1 percent (most preferably at least 3 percent) of the total silver precipitated in forming the silver iodochloride grains. Preferred contrast enhancing concentrations of the NZ dopants range from 1xc3x9710xe2x88x9211 to 4xc3x9710xe2x88x928 mole per silver mole, with specifically preferred concentrations being in the range from 10xe2x88x9210 to 10xe2x88x928 mole per silver mole.
Although generally preferred concentration ranges for the various SET, non-SET Ir and NZ dopants have been set out above, it is recognized that specific optimum concentration ranges within these general ranges can be identified for specific applications by routine testing. It is specifically contemplated to employ the SET, non-SET Ir and NZ dopants singly or in combination. For example, grains containing a combination of an SET dopant and a non-SET Ir dopant are specifically contemplated. Similarly SET and NZ dopants can be employed in combination. Also NZ and Ir dopants that are not SET dopants can be employed in combination. Finally, the combination of a non-SET Ir dopant with a SET dopant and an NZ dopant. For this latter three-way combination of dopants it is generally most convenient in terms of precipitation to incorporate the NZ dopant first, followed by the SET dopant, with the non-SET Ir dopant incorporated last.
The photographic elements of the present invention, as is typical, provide the silver halide in the form of an emulsion. Photographic emulsions generally include a vehicle for coating the emulsion as a layer of a photographic element. Useful vehicles include both naturally occurring substances such as proteins, protein derivatives, cellulose derivatives (e.g., cellulose esters), gelatin (e.g., alkali-treated gelatin such as cattle bone or hide gelatin, or acid treated gelatin such as pigskin gelatin), deionized gelatin, gelatin derivatives (e.g., acetylated gelatin, phthalated gelatin, and the like), and others as described in Research Disclosure I. Also useful as vehicles or vehicle extenders are hydrophilic, water-permeable colloids. These include synthetic polymeric peptizers, carriers, and/or binders such as poly(vinyl alcohol), poly(vinyl lactams), acrylamide polymers, polyvinyl acetals, polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetates, polyamides, polyvinyl pyridine, methacrylamide copolymers, and the like, as described in Research Disclosure I. The vehicle can be present in the emulsion in any amount useful in photographic emulsions. The emulsion can also include any of the addenda known to be useful in photographic emulsions.
The silver halide to be used in the invention may be advantageously subjected to chemical sensitization. Compounds and techniques useful for chemical sensitization of silver halide are known in the art and described in Research Disclosure I and the references cited therein. Compounds useful as chemical sensitizers, include, for example, active gelatin, sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhenium, phosphorous, or combinations thereof. Chemical sensitization is generally carried out at pAg levels of from 5 to 10, pH levels of from 4 to 8, and temperatures of from 30 to 80xc2x0 C., as described in Research Disclosure I, Section IV (pages 510-511) and the references cited therein.
The silver halide may be sensitized by sensitizing dyes by any method known in the art, such as described in Research Disclosure I. The dyes may, for example, be added as a solution or dispersion in water or an alcohol, aqueous gelatin, alcoholic aqueous gelatin, etc. The dye/silver halide emulsion may be mixed with a dispersion of color image-forming coupler immediately before coating or in advance of coating (for example, 2 hours).
Photographic elements of the present invention are preferably imagewise exposed using any of the known techniques, including those described in Research Disclosure I, section XVI. This typically involves exposure to light in the visible region of the spectrum, and typically such exposure is of a live image through a lens, although exposure can also be exposure to a stored image (such as a computer stored image) by means of light emitting devices (such as light emitting diodes, CRT and the like).
Photographic elements comprising the composition of the invention can be processed in any of a number of well-known photographic processes utilizing any of a number of well-known processing compositions, described, for example, in Research Disclosure I, or in The Theory of the Photographic Process, 4th edition, T. H. James, editor, Macmillan Publishing Co., New York, 1977. In the case of processing a negative working element, the element is treated with a color developer (that is one which will form the colored image dyes with the color couplers), and then with a oxidizer and a solvent to remove silver and silver halide. In the case of processing a reversal color element, the element is first treated with a black and white developer (that is, a developer which does not form colored dyes with the coupler compounds) followed by a treatment to fog silver halide (usually chemical fogging or light fogging), followed by treatment with a color developer. Preferred color developing agents are p-phetylenediamines. Especially preferred are:
4-amino N,N-diethylaniline hydrochloride,
4-amino-3-methyl-N,N-diethylaniline hydrochloride,
4-amino-3-methyl-N-ethyl-N-(xcex1-(methanesulfonamido) ethylaniline sesquisulfatie hydrate,
4-amino-3-methyl-N-ethyl-N-(xcex1-hydroxyethyl)aniline sulfate,
4-amino-3-xcex1-(methanesulfonamido)ethyl-N,N-diethylaniline hydrochloride and
4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluene sulfonic acid.
Dye images can be formed or amplified by processes which employ in combination with a dye-image-generating reducing agent an inert transition metal-ion complex oxidizing agent, as illustrated by Bissonette U.S. Pat. Nos. 3,748,138, 3,826,652, 3,862,842 and 3,989,526 and Travis U.S. Pat. No. 3,765,891, and/or a peroxide oxidizing agent as illustrated by Matejec U.S. Pat. No. 3,674,490, Research Disclosure, Vol. 116, December, 1973, Item 11660, and Bissonette Research Disclosure, Vol. 148, August, 1976, Items 14836, 14846 and 14847. The photographic elements can be particularly adapted to form dye images by such processes as illustrated by Dunn et al U.S. Pat. No. 3,822,129, Bissonette U.S. Pat. Nos. 3,834,907 and 3,902,905, Bissonette et al U.S. Pat. No. 3,847,619, Mowrey U.S. Pat. No. 3,904,413, Hirai et al U.S. Pat. No. 4,880,725, Iwano U.S. Pat. No. 4,954,425, Marsden et al U.S. Pat. No. 4,983,504, Evans et al U.S. Pat. No. 5,246,822, Twist U.S. Pat. No. 5,324,624, Fyson EPO 0 487 616, Tannahill et al WO 90/13059, Marsden et al WO 90/13061, Grimsey et al WO 91/16666, Fyson WO 91/17479, Marsden et al WO 92/01972. Tannahill WO 92/05471, Henson WO 92/07299, Twist WO 93/01524 and WO 93/11460 and Wingender et al German OLS 4,211,460.
Development is followed by bleach-fixing, to remove silver or silver halide, washing and drying.
Example of Dye Synthesis
Quaternary salt intermediates and dyes were prepared by standard methods such as described in Hamer, Cyanine Dyes and Related Compounds, 1964 (publisher John Wiley and Sons, New York, N.Y.) and The Theory of the Photographic Process, 4th edition, T. H. James, editor, Macmillan Publishing Co., New York, 11977. For example, (3-Bromopropyl)trimethylammonium bromide was obtained from Aldrich. The bromide salt was converted to the hexafluorophosphate salt to improve the compounds solubility in valeronitrile. Reaction of a dye base with 3-(bromopropyl)trimethylammonium hexafluorophosphate in valeronitrile at 135xc2x0 C. gave the corresponding quaternary salt. For example, reaction of 2-methyl-5-phenylbenzoxazole with 3-(bromopropyl)trimethylammonium hexafluorophosphate gave 2-methyl-5-phenyl-(3-(trimethylammonio)propyl)benzoxazolium bromide hexafluorophosphate. Which could be converted to the bis-bromide salt with tetrabutylammonium bromide. Dyes were prepared from quaternary salt intermediates. For example see the procedures in U.S. Pat. No. 5,213,956.
Example of Phase Behavior and Spectral Absorption Properties of Dyes Dispersed in Aqueous Gelatin
Dye dispersions (5.0 gram total weight) were prepared by combining known weights of water, deionized gelatin and solid dye into screw-capped glass vials which were then thoroughly mixed with agitation at 60xc2x0 C.-80xc2x0 C. for 1-2 hours in a Lauda model MA 6 digital water bath. Once homogenized, the dispersions were cooled to room temperature. Following thermal equilibration, a small aliquot of the liquid dispersion was transferred to a thin-walled glass capillary cell (0.0066 cm pathlength) using a pasteur pipette. The thin-film dye dispersion was then viewed in polarized light at 16xc3x97 objective magnification using a Zeiss Universal M microscope fitted with polarizing elements. Dyes forming a liquid-crystalline phase (i.e. a mesophase) in aqueous gelatin were readily identified microscopically from their characteristic birefringent type-textures, interference colors and shear-flow characteristics. (In some instances, polarized-light optical microscopy observations on thicker films of the dye dispersion, contained inside stoppered 1 mm pathlength glass cells, facilitated the identification of the dye liquid-crystalline phase). For example, dyes forming a lyotropic nematic mesophase typically display characteristic fluid, viscoelastic, birefringent textures including so-called Schlieren, Tiger-Skin, Reticulated, Homogeneous (Planar), Thread-Like, Droplet and Homeotropic (Pseudoisotropic). Dyes forming a lyotropic hexagonal mesophase typically display viscous, birefringent Herringone, Ribbon or Fan-Like textures. Dyes forming a lyotropic smectic mesophase typically display so-called Grainy-Mosaic, Spherulitic, Frond-Like (Pseudo-Schlieren) and Oily-Streak birefringent textures. Dyes forming an isotropic solution phase (non-liquid-crystalline) appeared black (i.e. non-birefrigent) when viewed microscopically in polarized light. The same thin-film preparations were then used to determine the spectral absorption properties of the aqueous gelatin-dispersed dye using a Hewlett Packard 8453 UV-visible spectrophotometer. Representative data are shown in Table A.
The data clearly demonstrate that the thermodynamically stable form of most inventive dyes when dispersed in aqueous gelatin as described above (in the absence of silver halide grains) is liquid crystalline. Furthermore, the liquid-crystalline form of these inventive dyes is J-aggregated and exhibits a characteristically sharp, intense and bathochromically shifted J-band spectral absorption peak, generally yielding strong fluorescence. In some instances the inventive dyes possessing low gelatin solubility preferentially formed a H-aggregated dye solution when dispersed in aqueous gelatin, yielding a hysochromically-shifted H-band spectral absorption peak. Ionic dyes exhibiting the aforementioned aggregation properties were found to be particularly useful as antenna dyes for improved spectral sensitization when used in combination with an underlying silver halide-adsorbed dye of opposite charge.
Photographic Evaluation